“The research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality [death],” study co-author Eileen Crimmins, the AARP Chair in Gerontology at the University of Southern California, said in a university news release. “However, we also propose that at older ages, it may be important to avoid a low-protein diet to allow the maintenance of healthy weight and protection from frailty.”

It found that 50-year-olds who got more than 20 percent of their calories from animal protein, particularly meat and dairy products had an increased risk of death from cancer or diabetes. This increased risk of death was much lower, or even non-existent, for 50-year-olds who ate a diet high in protein sourced mainly from plants.